<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">
    <!-- <meta name="viewport" content="width=device-width, initial-scale=0.5, maximum-scale=0.5, minimum-scale=0.5, user-scalable=no"> -->
    <!-- <meta name="viewport" content="width=device-width, initial-scale=0.3333333, maximum-scale=0.3333333, minimum-scale=0.3333333, user-scalable=no"> -->
    <title>3.1 通用适配原理</title>
    <style>
        * {
            box-sizing: border-box;
            padding: 0;
            margin: 0;
        }

        .header-container {
            width: 100%;
            height: 2.5rem;
            background-color: rgba(222, 24, 27, 0.9);
            /*1px边框*/
            border-bottom: 1px solid #000;
        }
    </style>
    <script>
        (function () {
            'use strict';

            setRemUnit();

            window.addEventListener('resize', setRemUnit);

            function setRemUnit() {
                var docEl = document.documentElement;
                var ratio = 18.75;
                var viewWidth = docEl.getBoundingClientRect().width || window.innerWidth;

                docEl.style.fontSize = viewWidth / ratio + 'px';
            }
        })();
    </script>
</head>
<body>

    <header class="header-container"></header>

</body>
</html>